Buzzing P-Bass Pickup on Whamola

I've just completed a Whamola (imagine, 1-string bass with a single p-bass pickup and volume knob and jack socket), and it all works great except there is an annoying buzzing from the pickup - this is either because I used a cheap pickup or maybe due to the wiring? The ground is just soldered onto the back of a metal piece that hides the wires, but also houses the jack socket (maybe causing some kind of feedback?). See pic below...

I may be mistaken but what you have here is the equivalent of a single coil alone. I think what you're hearing is 60 cycle hum and I don't think theres a lot to do to stop it, except maybe put the other half of the pickup in there, because the P-pickup use the two halfves of the pickup to cancel each other that's what make it an humbucker...

your "bridge" needs to move up the neck a little so that the string doesn't rest on its silks...I'd make sure that hole was fully de-burred, too...(a small round file will do the trick, or a dremel with a grinding tip)...

once you've done that...solder a ground wire from the bridge, to the ring of the jack...

that'll help heaps...also you can put a grounded metal plate behind the pickup.